It is common place for workers whose occupations require the worker to be exposed to radiation to wear a dosimeter for monitoring the extent of the worker's exposure. The dosimeters are constructed from materials that record the passage of energetic particles through the material. The response of these materials depends both on the type of radiation passing there through and the energy of the radiation. Early radiation dosimeters were constructed from photographic film. After the film was exposed to the radiation field, the film was developed and the degree of "fogging" of the film determined by measuring the opacity of the developed film. While this type of device is relatively cheap, it has low sensitivity to neutron radiation and requires a significant amount of processing to read-out the amount of radiation to which the worker was exposed.
More recent dosimeter designs utilize TL (thermoluminescent) phosphor elements to detect radiation in the dosimeters. These TL elements generate a light signal when heated. The light signal depends on the degree of exposure of the element to various types of radiation prior to the heating operation. These elements have higher sensitivities to neutron radiation and require less processing than photographic film based elements; hence, these elements have become widely used in dosimeters.
If the worker is exposed to a single type of radiation at a single energy, a single dosimetric element constructed from one of these TL materials could be used to measure the worker's exposure. However, such exposures are rare. In general, a worker is exposed to a mixed radiation field including two or more types of radiation. Mixed field dosimeters are typically constructed from a plurality of dosimetric elements having differing responses to the components of the mixed radiation field. A typical dosimetric element includes a TL element and a filter element. The filter element preferentially removes incident radiation of a particular type. For example, a filter element constructed from Cd preferentially removes thermal neutrons. By combining the measurements made with the various dosimetric elements, the radiation exposure of the worker arising from the mixed radiation field can be calculated. Radiation monitors for measuring the exposure of a worker in a photon-beta field typically require four such dosimetric elements. Similarly, the exposure of a worker to a neutron-photon field may be obtained with the aid of a four element detector.
A worker exposed to a mixed neutron-photon-beta field typically wears two four-element detectors to adequately measure the workers exposure. It would be desirable to reduce the number of dosimetric elements that must be processed to provide the exposure data for each worker in such mixed fields.
Attempts to construct a single four element monitoring device with satisfactory response in a mixed neutron-photon-beta field have been unsatisfactory. While four element detectors may be used in some mixed fields, unsatisfactory error rates are found to occur if the mixed field includes significant quantities of thermal neutrons.
Broadly, it is the object of the present invention to provide an improved radiation dosimeter that may be used in mixed neutron-photon-beta fields.
It is a further object of the present invention to provide a dosimeter that requires only four dosimetric elements in most practical fields.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.